Qingdao, China, may be more familiar to you as Tsingtao, as in Tsingtao beer. The city was a German colony for a couple of decades around the turn of the 20th century, and one of the first things they did was brew beer. The Germans used nearby Mount Fushan as a defense against the British colonial forces who wanted their piece of China. Darmon Richter got a chance to explore Mount Fushan and found plenty of tunnels, chambers, and bunkers from that era.
Torches switched to full-beam we stepped out of the storm, and into a still darkness.
The tunnel beyond was mostly formed from natural rock - the bulging contours of the passage illustrating where one crater at a time had been blasted into the solid rock, joining to form a corridor. Inside, nothing stirred... other than the slow, methodical dripping of condensation from the walls. Even the raging storm outside became inaudible, as we carefully made our way deeper inside the mountain.
Branching out from this main tunnel were a number of smaller caverns and chambers; some appeared to be no more than an accidental blast in the wrong direction, while others were reinforced with solid metal walls and bulkheads.
These chambers were often marked with Chinese characters scrawled clumsily across doorframes, and would have served as storerooms, ammo dumps, dormitories. At a humidity level not far off 100%, every surface was damp to touch - and the insides of these vaulted metal chambers sparkled like electric silver where the moisture ran down over mineral deposits.